Honing or grinding tool and measuring device for measuring wear

ABSTRACT

A honing or grinding tool and a measuring device used therewith is  descri The honing tool includes a cutting element, a cutting element support and a layer disposed between and connecting the cutting element and the cutting element support. The layer includes a substance embedded therein which selectively absorbs and/or emits electromagnetic radiation at specific wavelengths, such that the substance is exposed when the cutting element is worn off and detected by the measuring device.

BACKGROUND OF THE INVENTION

The invention relates to a honing or grinding tool, comprising a cuttingelement, a cutting element support for the cutting element, and ameasuring device for measuring wear of such tools.

Such tools are known. They are tools for machining by chip removalwherein a cutting layer (cutting element) is disposed on a steel base(cutting element support) by means of an adhesive layer.

In connection with the installation of fully automatic machiningoperations, primarily with multi-spindle machines, monitoring for wearis of great importance for operational safety and manufacturing quality.Wear of a honing bar is to the greatest extend dependent on the numberof pieces machined (tool life quantity). Other effects are, for example,feed, material hardness or non-homogeneity of the tool. Tool replacementat the right time is very important for efficient manufacturing. Itshould not be performed too early, i.e. when the volume of the cuttingmeans (volume of the cutting element or cutting layer) has not yet beenfully used up; nor should it be performed too late, because this wouldmean a run with tools no longer of qualitatively high value, i.e.rejects.

Up to now it was possible to monitor the wear of the cutting element ofa honing bar or a grinding wheel, for example approximately, in that inthe simplest case the shortest tool life (time for machining one workpiece) or tool life quantity (number of the work pieces machined) wasdetermined and this value was made the standard for checking of themachine tool by the operators at corresponding intervals. Checkingitself was performed by visual inspection of the tool.

Another possibility, in case of electronic-mechanical orelectronic-hydraulic feed of the tools, lies in monitoring the feedtravel. However, this means only indirect checking of wear of thecutting layer of a honing bar. If feeding is performed in steps by meansof a defined number of pulses, it is possible, corresponding to theassumed wear, to also provide after a predetermined number of workcycles fixed predetermined number of additional feed pulses. Such adevice also does not constitute actual wear monitoring, but merelycompensation for wear. Only the sum of the additional pulses requiredfor compensation and the comparison with an empirically set useablethickness of the cutting layer of a honing bar, however, will result ininformation as to whether replacement of a honing bar is needed, whichcan be processed by an automatic control.

In modern automatic controls the usable thickness of the cutting layer,the number of steps per compensating operation and the approach angle ofa honing tool are input in the control. The machine is stopped when itreaches the wear limit, based on the addition of the compensationdistance. The wear condition of the honing bars is displayed on amonitor by means of bar graphs. When reaching a programmable warninglimit the automatic control alerts the operator in good time to replacethe tool. However, this tool wear monitoring can only be employed incase of feeding by means of a step motor. This indirect wear monitoringcannot be used with hydraulic feeding. Furthermore, this indirectmonitoring has the disadvantage of having to take into accountmanufacturing tolerances in regard to height. But such a height mayunder certain circumstances correspond to a tool life quantity of up toseveral thousand work pieces. Thus indirect wear monitoring does notguarantee the best possible efficient use of the cutting layer.

No honing bars are known in which the wear condition can be directlydetermined. Tools for machining of workpieces by chip removal are knownfrom related fields, where wear monitoring is performed. However, thetechnologies used there cannot be directly used for the manufacture of ahoning bar in connection with which direct wear monitoring can beperformed.

For example, in EP-A-0 225 300 a throw-away carbide indexable insert isdescribed, where a layer impervious to radiation is disposed on asubstrate emitting radiation. With increased wear the substrate emittingradiation is increasingly exposed in the area of the flank. Theradiation emitted by the substrate is determined as a measurement ofwear. It is furthermore known from this reference to detect wear oversmall areas of the crater-wear type on the cutting edge itself. Thedirect wear monitoring by way of flank wear is impossible to apply inconnection with honing bars, because they are in contact with theworkpiece over large areas and have no flanks on which wear could bedetected in this manner.

The same is true for DD-A-222 414. A method for detecting wear of alathe chisel is described, in which a dot-shaped radioactive marker isapplied to the flank and/or cutting edge of the tool. The radioactivemarker wears off along with general wear. The change in radiation causedby this is used to measure wear. Aside from the not inconsiderableradiation exposure of the work place, such wear measuring is not usablewith honing bars, because two-dimensional monitoring of the cuttingelement is not possible.

It is known from the German Journal "Fertigungstechnik und Betrieb"[Manufacturing Techniques and Operation] (1985) 9, pp. 523-526, inparticular page 524, to coat the flank of a throw-way carbide indexableinsert with a radioactive marking. Again, Wear detection takes place bymeasuring the flank wear. This method, too, besides the radiationexposure, is not usable for honing bars because these have no flanks.The same holds true for the measuring principle, alternatively cited inthis publication, for the application of guideway structures at theflanks, which give off a signal when bonding because wear occurs. Honingand grinding tools are both tools with undeterminate cutting geometry inwhich flanks generally do not exit, contrary to throw-away carbideindexable inserts, drill or lathe chisels.

A drill is known from U.S. Pat. No. 4,420,253, into the shaft of which aglass fiber has been inserted. One end of the glass fiber is illuminatedby a light source. The other end extends into the shaft and terminatesat a set distance from the cutting edge. After the material locatedbetween the fiber end and the cutting edge has worn off, the light isregistered in a detector located underneath the drill. Wear monitoringof a homing bar is not possible with such a method, because the entirearea of the cutting element could only be monitored at excessive cost.

From German Published, Non-examined Patent Application DE-OS 34 04 257 ameasuring device is known for measuring the wear on a knife for cuttingsemiconductor plates. In this publication the light beam, originating inan emitting device and reflected by the knife, is registered in adetector. Wear of the knife element results in a change of thereflective behavior of the knife. For this reason the intensity of thereflected light beam also changes. This measuring device has thedisadvantage of being very susceptible to scattered light of otherradiation sources. As recited in this reference, the measuring devicedoes not function if the knife is wetted by a rinsing and/or coolingmedia. Furthermore, the measuring device only supplies a signal, becauseof the rotation of the knife, corresponding to a mean wear detected overa partial area of the knife.

Even if the mentioned disadvantages were accepted, such a method wouldin principle not be usable for honing and grinding tools, because wearof these tools cannot be definitely assigned to the reflective behaviorof the cutting element at the time, otherwise determinable with relativeaccuracy, when they need to be replaced.

In U.S. Pat. No. 4,031,368 a measuring device on a machine tool isdescribed wherein a laser beam is guided across the tool. The reflectionof the laser beam is registered in a receiver arrangement and passed onto an evaluation device. This evaluation device computers wear fromoptical measurement data, combined with other parameters (for example,size of the workpiece, vibrations, roughness of the surface, and thelike). This measuring device requires expensive andmaintenance-intensive devices, such as a laser resonator. For thereasons already mentioned above, it is not useful for detecting wear onhoning bars.

SUMMARY OF THE INVENTION

It is an object of the invention to improve a honing or grinding tool ofthe type mentioned above so that it becomes possible to detect the wearcondition of the cutting element directly, i.e. to determine when thecutting element is used up, so that replacement of the honing bar isrequired. The cutting layer of a honing bar or grinding wheel, formed byadhesive material containing diamond grains, is understood to be the"cutting element". Furthermore, the honing bar should be designed insuch a way, that monitoring of irregularities of the cutting layer isindependent, i.e. it should be possible, in spite of such irregularitiesin the height of the cutting layer, to exactly determine the correcttime for changing tools. Wear measurement at the honing bar by means ofthe measuring device described should also function if the honing bar iswetted by a rinsing or cooling media (for example honing oil).Furthermore, a suitable measuring device for measuring wear on such ahoning or grinding tool is to be provided, by means of which the wearcondition can be detected simply and directly, i.e. it can be determinedwhen the cutting element is worn out and replacement becomes necessary.

This object is attained by means of the invention by a honing orgrinding tool of the type previously described, in which between thecutting element and the cutting element support a substance is disposed,which selectively absorbs and/or emits electromagnetic radiation atspecific wave lengths and is embedded in the form of a layer in anotherlayer of a different material or is disposed as a layer on an indicatorsupport placed as a discrete element below the cutting element.

A measuring device for measuring wear on a honing or grinding tool ofthe type mentioned is characterized in that an emitter arrangementemitting a selective light radiation, is disposed focused on the cuttingelement, and in that furthermore a receiver arrangement, receivingselected radiation, is disposed focused on the honing tool in such away, that it receives the radiation directed on the tool by the emittingarrangement and reflected by the tool, and in that it derives a displaysignal therefrom.

As soon as the "cutting element", i.e. The cutting layer of a honing barhas worn off, the selectively absorbing and/or emitting substancedisposed underneath it is exposed. This can be detected withoutcomplicated evaluation of the radiation and in this way assigned to theextent of wear, which necessitates a changing of the tool, and a signalcan be derived from this, which either informs the operator or causes anautomatic exchange of the tool. The measuring device furthermore has theadvantage that measurement is not sensitive to scattered light fromother radiation sources, unwanted reflections, including those from thesurface of the cutting element, etc. Screening devices are thereforeunnecessary. Measurements can be taken directly at the tool under normalworking conditions. The measuring operation also functions if the honingbar or grinding wheel are wetted by a rinsing and/or cooling media.

Exemplary embodiments of the invention and its advantageous improvementswill be described below by means of the attached drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a cross section of an exemplary embodiment of a tool;

FIG. 2 illustrates an exemplary embodiment of a measuring device;

FIG. 3 illustrates the disposition of a measuring device in accordancewith FIG. 2 on a honing tool;

FIG. 4 illustrates a cross section of a second exemplary embodiment of atool;

FIG. 5 illustrates a cross section of a die for manufacturing a tool inaccordance with FIG. 4;

FIG. 6 illustrates a step in the manufacture of a further exemplaryembodiment of a tool in accordance with the invention;

FIG. 7 illustrates a cross section of a further exemplary embodiment ofa tool;

FIG. 8 illustrates a top view of the tool in accordance with FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A honing bar 1 (FIG. 1) is formed by a cutting layer 2, an adhesivelayer 3 and a steel base 4. Customarily the steel base is approximately1 to 3 mm thick, the adhesive layer customarily 0.1 to 0.2 mm. It iscomposed of binder material as well as several nonferrous metals (forexample copper, zinc, tin). The cutting layer consists of bindermaterial with diamond grain, having a diameter of 7 to 400 μm and at aconcentration of 1 to 200 carat/cm³, embedded in it. Such honing barsare sintered at temperatures of 700° to 1,000°.

In the exemplary embodiment in accordance with FIG. 1, a fluorescingdye, shown in the form of powder particles 5, is embedded in theadhesive layer 3 at a ratio of two parts binder power to one part dye.Fluorescing dyes which can withstand high temperatures and are non-toxicare known from the cosmetics and printing trade. They are obtained bymeans of so-called fluorophores.

FIG. 2 shows a measuring device for measuring the wear of a honingbar 1. If the cutting layer 2 has worn off to the point that theadhesive layer 4 containing fluorescing dye is exposed, the followingcan be noted:

A measuring device 10 has been provided for this purpose on therespective machine tool (honing machine, grinding machine). It has anemitter device giving off selective radiation, formed by a radiationsource 11, filter 12 and a lens arrangement 13 for focusing the emittedradiation. The focused radiation impinges on the honing bar 1, i.e.after the cutting layer 2 has worn off, on the adhesive layer 3containing the fluroescing substance 5. Furthermore, a receiving devicehas been provided, comprising a lens arrangement 14, filters 15 andcorresponding photodiodes 16. The photodiodes 16 are a detector, i.e. acomponent the electrical signal of which is determined by the impingingradiation. The emitter device and the receiving device are such that theradiation emitted by the substance 5 when it is excited by the emitterdevice is received by the receiving device. Only one filter 12 or 15each has been shown in the drawings. This was done for the sake ofclarity of the drawing itself. To detect the individual wave lengths ofthe specific spectra, it is possible to provide several coordinatedfilters 12 or 15 with associated lenses.

The filter 12 is designed such that a specific distribution ofwavelengths (spectrum) from the radiation source 11 remains, whichreaches the surface of the tool 1. This radiation is called excitationradiation, for example with wavelengths from 254 to 366 nm. Whenimpinging on the fluorescing substance embedded in the form of powderparticles 5 in the adhesive layer 3, it causes an emission radiationhaving a different wavelength distribution (spectrum), for example withwavelengths of 490, 530, 610 nm.

The excitation radiation of a certain spectrum may be generated eitherby the radiation source 11 itself already emitting a correspondinglyselective spectrum (for example a mercury low pressure radiator).Another possibility, such as shown in FIG. 2, consists in interposingbetween the radiation source and the surface to be excited by theexcitation radiation corresponding filters 12, the transparency of whichis correspondingly selectively adjusted. Thus the filters 15 areadjusted in such a way that they only let through radiation of thecorresponding emission spectrum. In this way it is absolutely assuredthat only the radiation caused by the fluorescence of the fluorescingdye in the adhesive layer 3 reaches the photodiode 16 and causes acorresponding electrical signal there. Such a device is impervious toany other radiation (scattered light from other radiation sources,unwanted reflections, etc).

A further receiver in the form of a photodiode 21 is provided parallelto the emitter/receiver arrangement, which directly receives theradiation emitted by the radiation source 11. The signals from bothphotodiode arrangements 16 and 21 reach a quotient generator 22. Itsupplies the ratio of both signals. In this way it is assured thatvariations in the illumination intensity (caused, for example, byvariations in the power supply) are not included in the final signalemitted by the quotient generator 22 on the line 23. The signal at theoutput of the quotient generator 22 reaches a personal computer PC forevaluation and/or registration. Signals, for example "early warning","earliest time for replacement", "latest time for replacement", are sentvia further liens 24, 24' 24".

FIG. 3 shows the arrangement of the measuring device 10 in the vicinityof a honing tool 30, along the circumference of which a plurality ofhoning bars 1 have been disposed.

In FIG. 1 the fluorescing dye is mixed into the adhesive layer 3 in theform of powder particles 5, which is exposed as soon as the cuttinglayer 2 has worn off. FIG. 4 shows another embodiment of the honing bar.There the adhesive layer 3 is provided with a groove 40 prior to theattachment of the steel base 4. This is cut sufficiently deep so that itjust extends into the surface of the cutting layer 2 or adjoins it insuch a way that the groove is open towards the outside after the cuttinglayer 2 has worn off. The groove itself has a cross section of, forexample, 0.3×0.3 mm. A copper wire 41 is inserted into this groove as inindicator carrier; as indicator it has a layer 42 of fluorescing dye.The layer may be approximately 0.1 mm thick. First (see FIG. 6), astructural part 43, comprising adhesive layer 3 and cutting layer 2, ismade, into which a groove 40 is punched with the aid of a die 44, shownin cross section in FIG. 5. The copper wire 41 is then placed into thisgroove. Then the steel base 4 is pressed on and the entire honing bar 1is sintered. The advantage of this device, compared with FIG. 1, is thatthere is no weakening of the cross section of the adhesive layer.

In accordance with FIGS. 7 and 8, after the entire honing bar 1 isfinished, a groove 50 is cut into the tool (for example by sparkerosion) from the side of the steel base 4 in such a way that the footof the groove just extends into the cutting layer 2 or borders againstit and exposes the groove 50 from this end when the cutting layer 2 isworn off. A fluorescing dye 5 is then inserted into this groove. Thegroove then is covered with solder 51. In this connection it isadvantageous that the dye need not be exposed to the temperature andpressure of a sintering process because it is only inserted afterwards.In place of a groove it is also possible to provide a bore. In general,it should just be a recess extending up to the cutting layer.

It is important that after the cutting element has worn off, a substanceis exposed the appearance of which can be selectively detected. This canbe done not only through measuring selective emitted radiation, but alsoby measuring selective absorption. In general the measuring device 10 isa photometric device, with the inclusion of the selectively absorbingand/or emitting substance, in the tool in the form of anemitter/receiver arrangement. Alternately to the fluorometric methodshown, detection of the absorption of infrared radiation or UV radiationis possible. With all radiation it is particularly advantageous if it isnot visible light in order to eliminate the effects of scattered orsecondary light.

In all these way sit is possible to obtain a faultlessly operatingmeasuring device suitable for the auto-identification of worn tools(honing bars, grinding wheels).

What is claimed is:
 1. A cylindrical honing or grinding tool,comprising:at least one cutting element having an extent in thecircumferential direction of the tool; a steel base cutting elementsupport for each cutting element; and an adhesive layer disposed betweenand connecting each cutting element and its respective cutting elementsupport, each said adhesive layer having a fluorescing substanceembedded therein which selectively absorbs and/or emits electromagneticradiation at specific wavelengths, such that the fluorescing substanceis exposed when the cutting element is worn off, said fluorescingsubstance after being excited by a first set wavelength distributionemitting radiation of a second set wavelength distribution.
 2. Thehoning or grinding tool as defined in claim 1, wherein said fluorescingsubstance absorbs UV radiation.
 3. The honing or grinding tool asdefined in claim 1, wherein said fluorescing substance absorbs infraredradiation.
 4. A honing or grinding tool, comprising:a cutting element; acutting element support; and a layer disposed between and connecting thecutting element and the cutting element support, said layer having arecess formed therein within which an indicator carrier surrounded by afurther layer is embedded, said further layer having fluorescingsubstance therein, such that the substance is exposed when the cuttingelement is worn off.
 5. The honing or grinding tool as defined in claim4, wherein the indicator carrier comprises a wire.
 6. The honing orgrinding tool as defined in claim 5, wherein the wire is of non-ferrousmetal.
 7. The honing or grinding tool as defined in claim 4, wherein therecess comprises a groove which extends into said cutting element, saidcutting element support and said layer.
 8. The honing or grinding toolas defined in claim 4, wherein the cutting element comprises a cuttinglayer, the cutting element support comprises a steel base, and the layerdisposed between the cutting element and the cutting element supportcomprises an adhesive layer.
 9. The honing or grinding tool as definedin claim 4, wherein said substance, after being excited by a first setwavelength distribution, emits radiation of a second set wavelengthdistribution.
 10. The honing or grinding tool as defined in claim 4,wherein said fluorescing substance comprises a substance which absorbsUV radiation.
 11. The honing or grinding tool as defined in claim 4,wherein said fluorescing substance comprises a substance which absorbsinfrared radiation.